Reinforced concrete body



J n- 7, 1947. K. P. BILLNER 2,414,011

REINFORCED CONCRETE BODY Original Filed June 7, 1942 Patented Jan. 7,1947 REINFORCED CONCRETE BODY Karl P. Billner, Tampa, Fla.

Original application June 7, 1942, Serial No.

Divided and this application March 447,047. 16, 1943, Serial No. 479,381

9 Claims. 1 This invention relates to reinforced plastic bodies.

The formation of cracks in concrete structures has always been aparticularly troublesome problem. By its very nature, concrete isintended to assume compressive stresses only, while its reinforcingelements arerelied upon to receive the tensile stresses. Yet aninevitable tendency accompanying the setting and hardening of concreteis the formation of internal stresses which are in turn responsible forthe objectionable cracking. Among the various proposals for overcomingthese effects is what is known as prestressing.

In concrete ships, for example, it has been considered advisable in thepast to permit only very low working stresses in the steelreinforcement, since with higher stresses, small cracks have beenobserved in the concrete in portions of the ship which are subjected totension. By way of contrast, much higher stresses have been permitted inordinary concrete structures, such as buildings, whereby the propertiesof the steel reinforcement are utilized to much greater advantage. But,by prestressing the reinforcement, cracks and fissures can be avoided,air and water tightness achieved, and economy in reinforcement realized.Hence the use of prestressing adapts itself admirably to ship, tank andsimilar construction.

The advantages of prestressing reinforced plastic bodies, particularlyconcrete, have been known to the engineering profession for many years.Yet in spite of the appreciable thought and effort which have beenexpended in attempting to reduce this knowledge to a practicable basis,there has been no widespread adoption of any method thus far proposed.Most of the previously known methods have been directed along the linesof physically stretching the reinforcing elements, pouring the plasticmaterial about them, allowing the material to harden and then releasingthe reinforcing elements and permitting their contracting force to setup compressive stresses in the concrete. These methods have been fraughtwith difliculties in applying the tensile stresses and in regulating themagnitude of the forces which are ultimately imposed upon the hardenedbody.

It has been proposed also to prevent a bond between concrete and itsreinforcing elements by coating the reinforcing bars with petroleum orasphaltic materials as described in the patents to Dill, No. 1,684,663,dated September 18, 1928, and Hewett. No. 1,818,254, dated August 11,1931;

and by surrounding the reinforcing bars with metal tubes as disclosed inthe patent to Kennedy, No. 2,185,749, dated January 2, 1940. And inthe'patent to Steiner, No. 903,909, dated November 17, 1908, theprogressive tensioning of reinforcing elements while'the concrete ishardening has been described. Prestressing of reinforcing elements priorto pouring concrete about them has also been proposed by Freyssinet inBritish Patent No. 338,864, dated June 18, 1929, wherein the elementsare expanded by the heating effect of an electric current passedtherethrough.

In accordance with the present invention, the eilects of prestressingare obtained by thermally expanding the reinforcing elements after theplastic body has hardened. This is accomplished by forming the plasticbody about the reinforcing element and releasing the bond between thebody and the element so that the element may be expanded with respect tothe body, whereupon. the element is permitted to partially contract soas to bear upon the body and produce compressive stresses therein.

The reinforcing element is expanded prefer-" Y material is utilized sothe heating effect will soften it to permit the reinforcing element toexpand. Under some circumstances, thermosetting materials will be used.Where there is danger of short circuiting or leakage, the cover-- ingmaterial may be electrically insulating, but in other cases, low meltingmetals or alloys may serve satisfactorily. The covering or coatingmaterials should have melting or at least softening points which aresufliciently low as to permit the desired results without requiring thetemperature of the reinforcing elements to be raised to a degree thatwould adversely affect their reinforcing characteristics. And themelting or softening point is also preferably above atmospherictemperatures to which the structure will ordinarily be exposed.

When the reinforcing element has expanded an amount sufiicient to imposethe desired stresses upon subsequent contraction, it is suitably securedagainst excessive contraction so that the desired amount of itscontracting force will be applied to produce compressive stresses withinthe body. The mode of securing the element may vary according to thetype of structure involved, but such expedients as welding, clamping,threading and pinning suggest themselves. Where the securing arrangementemployed requires a recess in the concrete body, for ex:

ample, a dry packed concrete filling may be used to protect the Jointand to impart to the structure a finished appearance.

A thermoplastic material such as sulfur, melting at approximately 120 C.is a good electrical insulator and at the same time furnishes areasonably good bond between steel and concrete. In some cases, thethermoplastic or thermosettlng covering or sheathing material may assumea preformed tubular shape.

For purposes of illustration, reference is made to the accompanyingdrawing wherein:

Fig. 1 is a sectional elevation of a reinforced member embodying thepresent invention;

Fig. 2 is a sectional elevation of an arcuate member;

Fig. 3 is a sectional elevation of a helically reinforced cylindricalbody;

Fig. 4 is a sectional elevation of a cylindrical body containing anannular reinforcing element; and

Fig. 5 is a perspective of a clip for securing the ends of thereinforcing elements of Figs. 3 and 4.

The plastic body In, depicted as concrete in the drawing, is providedwith one or more reinforcing elements I2, and each element is covered bya material H which prevents a direct bond between the plastic body andits reinforcement. Where the plastic body is thermoplastic itself orwhere it possesses no tendency to adhere to the reinforcing element, theinterposed material Il may be omitted. But since concrete and steel havebeen indicated in the various figures of the drawing, the interposedmaterial also has been indicated. Among the materials considered to besuited for interposition between the body and its reinforcement underproper conditions are sulfur. low melting resins, low melting alloys,various other thermoplastic and thermosetting substances, or othersuitable materials which may be wrapped, coated, molded or otherwiseformed about the reinforcing elements.

In Fig. 1, the body may represent a slab, beam, floor, deck, road, wall,or other member in which the effect of prestressing is desired. Afterthe concrete has hardened sumciently to resist substantial deformationupon application of the desired stresses, heat is applied to therenforcing element I! as by attaching electrical conductors to its endsand allowing a predetermined type and amount of current to flow so as tomelt or soften the interposed material I and to elongate or axiallyexpand the element [2 a desired amount. At this point the nuts I areadvanced a predetermined amount upon the threaded ends ll of therelatively smooth rod l2, so that when the thermal effect is reduced, asby decreasing the current flow, the rod will contract until the washersor hearing plates 20 engage the concrete body and the furthercontracting force of the reinforcing element will apply compressivestresses to the concrete body. Whereas but one reinforcing element hasbeenshown in Fig. 1, it will be understood that any number may beemployed depending upon the dimensions of the plastic body. the yieldpoint of the reinforcing elements and the stresses to be imposed. Suchadditional reinforcing elements may be arranged parallel to or at anydesired angle to the one shown.

Fig. 2 illustrates the invention as applied to an arcuate or curvedmember which may be an arch, floor, roof, wall, hull, or any reinforcedbody to which such a shape adapts itself. In this case, two reinforcingelements having threaded ends l8 and covered with sheathing material llhave been shown, provided with nuts I6 and bearin plates or washers 22.In this instance, the reinforcing elements may be heated and clampedsequentially or simultaneously, the mode of operation beingsubstantially the same as that described with reference to Fig. 1. I

Fig. 3 illustrates a cylindrical concrete body reinforced withoppositely directed helices 24, the opposed upper ends of which arejoined by welds 26 or other suitable means. In such an arrangement, thehelices are preferably heated simultaneously so that they will bothattain their desired degree of expansion at the same time, whereupontheir free ends provided with enlarged heads 28 are engaged by thebifurcated ends of a clip 32 of predetermined length or otherwisesuitably connected to restrict contraction. After the joints have beenmade, tendency of the helices to contract will cause the convolutions toembrace the adjacent concrete surfaces whereby the concrete body as awhole will be subjected to compressive stresses. As indicated by brokenlines, the joint at the lower ends of the helices may be formed withina. recess provided in the concrete body. Examples of structures to whichthis form of the invention may be applied include tanks, silos. linings,pipes, rings and other bodies.

Fig. 4 is directed to a cylindrical body of reinforced concrete whereinthe enlarged ends 28 of the reinforcing element l2 are received in arecess 30 which is formed to permit the joint to be made internally ofthe structure. When current is applied to the ends 28, the thermoplasticor other suitable material l4 will soften and the discontinuous annulusor hoop will expand axially. After expansion has progressedsuflicienily, the current is discontinued and a clip 32 havingbifurcated ends 34 is slipped over the enlarged heads 28. Then theelement l2 will partially contract and impose the desired compressivestresses upon the body of the plastic structure l2. If desired, therecess 30 may be filled with dry packed concrete 33 or the like toprovide the body with an unbroken periphery and also protect the jointagainst the elements.

Where thermoplastic or thermosetting covering materials are used, uponreduction of the thermal effects below their melting or softeningpoints, they will harden and effect a bond between the plastic body andits reinforcement. In connection with such covering materials, where itis desired to prevent undue abrasion during handling, a protectivesheath such as mesh or other suitable fabric may be employed, or asuitable substance such as asbestos fibers may be incorporated in thecovering material itself.

The heating current may be D. C. or A. C. of

desired frequency, and of various voltages as will be determined by theresistance of the reinforcing elements, desired degree of expansion andthe temperature limit to be observed to avoid injury to the propertiesof the steel or other materials.

Among the many uses to which the principles of the present invention maybe applied, there will be mentioned but a few, namely: bridges, roads,piles, floors, roofs, arches, walls. ship pipes,

tanks, silos, tunnel linings, dome foundation rings, columns, beams andslabs.

This application is considered to be a division of application SerialNo. 447,407, filed on June 1'7, 1942 (Patent No. 2,319,105)

The foregoing description is illustrative of the invention whose scopeis set forth in the following claims. 1

I claim:

1. A reinforced structure comprising a hardened plastic body having astressed reinforcing element therein normally subjecting said body tocompressive stresses, and a solidifying thermoplastic materialinterposed and effecting a rigid bond between said element and saidbody.

2. A reinforced concrete structure'comprising a hardened concrete bodyhaving a stressed reinforcing element therein-normally imposingcompressive stresses upon the concrete, and an electrical insulatingthermoplastic material effecting I a rigid bond between said element andsaid body.

3. A reinforced concrete structure comprising a hardened concrete body,a pretensioned reinforcing element having a bearing upon said body tomaintain a substantial portion thereof in compression, and a hardenedthermoplastic material rigidly bonding said element to said body.

4. A reinforced concrete structure comprising a hardened concrete body,a pretensioned reinforcing element having a bearing upon said body tomaintain a substantial portion thereof in compression, and a, hardenedthermosetting material rigidly bonding said element to said body.

5. A reinforced concrete structure comprising a hardened concrete body,a'pretensioned reinforcing element having a bearing upon said body tomaintain a substantial portion thereof in compression,'and a body ofhardened sulfur bonding said element to said concrete body.

6. A reinforced concrete structure comprising a hardened concrete body,a pretensioned reinforcing element having a bearing upon said body tomaintain a substantial portion thereof in compression, and ahardenedthermopla-stic material rigidly bonding said element to saidbody, said thermoplastic material having a melting point in excess ofatmospheric temperatures to which said structure is ordinarily exposed.

7. A reinforced concrete structure comprising a hardened concrete body,a pretensioned reinforcing element having a bearing upon said body tomaintain a, substantial portion thereof in compression, and a hardenedthermoplastic material rigidly bonding said element to said body, saidthermoplastic material having a melting point in excess of atmospherictemperatures to which said structure is ordinarily exposed and below"that which would adversely affect the properties of the reinforcingelement.

8. A reinforced concrete structure comprising a hardened concrete body,a pretensioned reinforcing element embedded within and having a bearingupon said body to maintain a substantial portion thereof in compression,and a hardened thermoplastic material surrounding said element andrigidly bonding it to said body.

9. A reinforced concrete structure comprising va hardened concrete body,a pretensioned reinforcing element having a bearing upon said body tomaintain a substantial portion thereof in compression, and a hardenedthermoplastic material interposed between said element and said body andserving as a rigid bond between them.

KARL P. BILLNER.

